Generally, ball valves have short switching times, low torques to drive the ball valves, and watertight structures. Therefore, the conventional ball valves are typically used to control flows of fluids. As shown in FIG. 1, a first conventional ball valve includes asymmetric first and second valve casings 10 and 20. A ball seat 11 is provided in the second valve casing 20. A ball 30 is seated in the ball seat 11.
A lever receiving hole 13 is provided on the second valve casing 20. A control lever 40 is inserted into the lever receiving hole 13 to be integrally coupled to the ball 30. The first conventional ball valve having the above-mentioned structure is interposed between two pipes to couple the two pipes to each other, thus controlling a flow of a fluid passing through the two pipes. When the control lever 40 is positioned in a same direction as the longitudinal directions of the two pipes, the ball valve is opened. When the control lever 40 is positioned in a direction perpendicular to the two pipes, the ball valve is closed.
However, in the first conventional ball valve, as shown in FIG. 1, shapes of the first and second valve casings 10 and 20 to receive therein the ball 30 are asymmetrical. Each of the first and second valve casings 10 and 20 is very complex in its construction. Therefore, it is impossible to manufacture the first conventional ball valve through an injection molding process. Only, the first conventional ball valve must be manufactured through a casting or cutting process. Thus, the first conventional ball valve increases the production costs thereof. Furthermore, a material of the first conventional ball valve is limited.
In the first conventional ball valve, in case that an error of the ball 30 is generated or an inspection of the ball 30 is necessary, a plurality of bolts must be loosened from the first and second valve casings 10 and 20. The first and second valve casings 10 and 20 are thereafter separated from each other. Thereafter, the control lever 40, which has been coupled to the ball 30 through the lever receiving hole 13, is removed from the second valve casing 20 having therein the ball 30. The ball 30 is, thereafter, removed from the second valve casing 20 to be inspected. As such, the first conventional ball valve is problematic in that a lengthy time is required to inspect the ball 30 due to the complicated disassembling process.
In an effort to overcome the problems experienced in the first conventional ball valve with the asymmetric first and second valve casings 10 and 20, a second conventional ball valve, which is made of a synthetic resin through an injection molding process, as shown in FIGS. 2 and 3, was proposed. Referring to FIGS. 2 and 3, the second conventional ball valve includes first and second valve casings 50 and 60 which have symmetric structures and each are manufactured through an injection molding process, and an intermediate casing 70 which is manufactured through an additional injection molding process. The second conventional ball valve further includes a ball 80 which is seated in the intermediate casing 70, and a lever receiving part 71 which is provided on a predetermined portion of the intermediate casing 70. A control lever 90 is inserted into the lever receiving part 71 and is coupled to the ball 80. A first ring 91 is seated in a ring-shaped groove which is provided on a pre-determined portion of the control lever 90.
An external thread is provided on an outer surface of the lever receiving part 71. The second conventional ball valve further includes a cap 92 which has on an inner surface thereof an internal thread. The cap 92 is threadedly fastened to the lever receiving part 71, thus preventing the control lever 90 from being undesirably removed.
The first and second valve casings 50 and 60 are coupled to the intermediate casing 70, with second and third rings 51 and 61 respectively interposed in junctions between the first and second valve casings 50 and 60 and the intermediate casing 70. At this time, the first and second valve casings 50 and 60 are coupled to the intermediate casing 70 by a plurality of longitudinal coupling bolts 72.
However, because the second conventional ball valve includes the three body parts which comprises the first and second valve casings 50 and 60 and the intermediate casing 70, the number of processes and a time required to manufacture the second conventional ball valve are increased. Furthermore, to couple or disassemble the second conventional ball valve having the three body parts, the second conventional ball valve forces a user to spend a lengthy working time and a great manual force. To seal the junctions between the three body parts and the control lever 90, the first, second and third rings 51, 61 and 91 must be respectively provided in the junctions. Even though the first and second rings 51 and 61 are respectively provided in the junctions between the three body parts, the water tightness of the junctions between the three body parts must be reduced while the three body parts are coupled to each other by the plurality of longitudinal coupling bolts 72.
In addition, to maintain a coupled state between the control lever 90 and the ball 80, the cap 92 is threadedly tightened to the lever receiving part 71. The tightening of the cap 92 to the lever receiving part 71 causes a defect in that the cap 92 and even the control lever 90 may be undesirably removed from the intermediate casing 70 due to wear of the thread of the cap 92 or the lever receiving part 71. To remove the ball 80 from the intermediate casing 70 for an inspection of the ball 80, one of the first and second valve casings 50 and 60 is separated from the intermediate casing 70. The cap 92 and the control lever 90 must be further separated from the intermediate casing 70, so that the structure of the second conventional ball valve having the three body parts causes inconvenience to a user.